Exercises

1. Specify the set of values and the set of operations provided by each of the following C++ built-in data types:
   1. char,
   2. int,
   3. double, and
   4. string.
2. What are the features of C++ that facilitate the creation of user-defined data types.
3. Explain how each of the following C++ features supports polymorphism:
   1. operator overloading,
   2. templates, and
   3. inheritance.
4. Suppose we define two concrete classes, A and B, both of which are derived from the Object class declared in Program . Furthermore, let a and b be instances of classes A and B (respectively) declared as follows:

   class A : public Object { ... };
   class B : public Object { ... };
   A a;
   B b;

   Give the sequence of functions called in order to evaluate a comparison such as ``a<b''. Is the result of the comparison true or false? Explain.
5. Consider the Wrapper<T> class defined in Program . Explain the operation of the following program fragment:

   int i = 5;
   Wrapper<int> j = 7;
   i = j;
   j = i;

6. There are three ways to test whether a given object instance, obj, is the null object:
   1. obj.IsNull ()
   2. obj == NullObject::Instance (), and
   3. &obj == &(NullObject::Instance ()).
   Discuss the relative merits of each approach.
7. Let c be an instance of some concrete class derived from the Container class given in Program . Explain how the statement

   cout << c;

   prints the contents of the container on the standard output stream, cout.
8. Suppose we have a container c (i.e., an instance of some concrete class derived from the Container class defined in Program ) which among other things happens to contain itself. Is it permissible for c to own the objects it contains? What happens when c's destructor runs if it owns the objects it contains.
9. Iterators and visitors provide two ways to do the same thing--to visit one-by-one all the objects in a container. Give an implementation for the Accept function of the Container class that uses an iterator.
10. Is it possible to implement an iterator using a visitor? Explain.
11. Suppose we have a container which we know contains only instances of the Int class defined in Program . Design a Visitor which computes the sum of all the integers in the container.
12. Explain what the following visitor does and why it is a horribly bad idea:

    class DeletingVisitor : public Visitor
    {
    public:
        void Visit (Object& object)
            { delete &object; }
    };

13. Consider the following pair of Associations:

    Association a (*new Int (3), *new Int (4));
    Association b (*new Int (3));

    Give the sequence of functions called in order to evaluate a comparison such as ``a==b''. Is the result of the comparison true or false? Explain.

Copyright © 1997 by Bruno R. Preiss, P.Eng. All rights reserved.